The hardware for Servo Tester 2 is only a suggestion, and you will most likely have to make some changes to it. The version shown here is the full blown, all features with bells and whistles. You can cut down on the features and component count if you like.
Click to enlarge
I use some quite special IC's, but some of them can be hard to find locally. Several of the sub-circuits can be made in more conventional ways. Like the LT1634. It is nothing more than a 4.096V voltage reference that I usually use for all my projects involving A/D converters. But this isn't a high-precision application, so a more simple reference is no big problem. You can even just use the 5V already available.
The LT1618 is a nice little switcher, that I fell in love with. It
is coupled in SEPIC mode (straight from the datasheet), and it
provides 5V from input voltages both lower and higher. This way the
AVR can get its needed 5V, while the tester is supplied from a
standard 4-cell receiver battery pack.
To avoid using the
switcher, you could use a standard 7805 linear regulator. Then you
would just need to have a 9V battery (or similar) at hand.
Or you
could use a Mega16L and completely skip the use of a regulator. The
Mega16L can run at supplies down to 2.7V. You would, however, be
overclocking it by 25%. I have heard of one that is going to try
this.
A third option could be to wait for the new Mega168. It is
designed to run at 10 MHz at voltages down to 2.7V. The Mega168 has
another pin layout, so you will need to rewrite some of the software,
if you go along this route.
Watch out for the display connections. I haven't used a LCD with the standard pinout. Instead I've used a real nice (but not so cheap) display from Conrad (order number 181755).
The rotary encoder is also from Conrad. Order number 705538. There
are plenty other types out there that can be used instead. It must be
an (rotationally) endless type with 2-bit Gray code / quadrature
output, with two detents/positions per signal cycle. It should
therefore have positions for the two outputs being both high and both
low. I recommend a 15/30 type, that is one with 15 full signal cycles
and 30 detents for a single 360 degree rotation.
The encoder is a
type with built-in pushbutton.
The rest of the components aren't critical in any way.
I haven't finished the tachometer circuit just yet. I hope it will be possible to make it work with the current layout. But don't take that for granted.
If the tester is built exactly as the schematic above, it may look like this:
This example PCB layout is available in the download section.